This invention pertains to a getter flasher having a movable, self-centering coil enclosure.
In manufacturing a cathode-ray tube, a getter material is disposed within the tube in a metallic container held by one end of an elongated, resilient support spring which is attached at the other end to a mount assembly so as to extend in cantilever fashion into a funnel of the tube. Such a combination of getter container and support spring is commonly known as an "antenna getter". After the tube is partially exhausted of gases and hermetrically sealed, the getter material is quickly heated until it vaporizes or "flashes" from its container, and then deposits as a getter film on internal surfaces of the tube. The length of the spring permits the getter container to be positioned well within the funnel, where the getter material can be flashed to provide optimum coverage and where the spring and container will be out of the paths of electron beams issuing from the mount assembly and not interfere with the operation of the tube. The getter material, typically a barium-aluminum alloy, has the property of sorbing gases remaining after exhausting the tube, or those later released by the walls of the tube, or by structural components therein. In both cases, the getter material acts as an auxiliary pump which provides the high vacuum needed for effective operation of the tube.
The getter material in the metallic container is flashed by positioning an rf (radio frequency) induction heating coil proximate that exterior surface of the cathode-ray tube which is opposite, or closely adjacent, the getter container, and then energizing the coil with an rf current. The alternating magnetic field generated by the energizing heating coil induces a current flow in the metallic getter container, heating the container and its contents to a high enough temperature to flash the contained getter material. In order to vaporize the maximum amount of getter material from the container and to realize a desired distribution of deposited getter material in the tube, it is necessary to position the heating coil properly with respect to the getter container so as to produce optimum magnetic coupling between them. The coil position is critical because the power delivered to the getter container varies with the inverse square of the distance between the coil and the container. Planar alignment between the container and the coil is also critical in order to properly intercept the transverse electric field, which is what heats the container. Misalignment may also cause severe localized heating which melts or softens the getter container and/or support spring, resulting in an unsatisfactory getter flashing step.
The getter flashing step is typically performed along a production line where a robot, or operator, places the cathode-ray tube into a fixture which holds the tube adjacent to a getter flasher. The presence of the tube in the fixture starts an rf generator which delivers power to a heating coil in the getter flasher. Since the fixture is designed for the rapid loading of many tubes which move along the production line at a high rate, a particular tube may not be properly seated in the fixture, causing the getter container and the heating coil to be out of alignment with each other. Also, slight changes in the contour of either the tube or position yoke, a hand-made part (which varies from one fixture to the next) on which the tube rests in the fixture, may result in the heating coil being improperly positioned with respect to the getter container. The present invention provides a getter flasher having a self-centering heating coil which is able to properly position itself with respect to the getter container in funnel-shaped tubes of different sizes and/or shapes.